Abstract

Rastrites maximus does not occur in the Birkhill Shales at Dob's Linn, the type locality for the Rastrites maximus Biozone. Indeed, the uppermost Birkhill Shales here yield a fauna typical not of the lower part of the Telychian (Upper Llandovery), the level at which the R. maximus Biozone or Subzone has traditionally been placed, but of the upper Aeronian (Middle Llandovery). R. maximus does occur in the Birkhill Shales to the south and east of Dob's Linn, however, where, as a result of the diachroneity of the base of the overlying Gala greywackes, the uppermost Birkhill Shales are younger than at Dob's Linn, being of lower Telychian age. In Wales R. maximus has not been found to be as useful in biostratigraphical studies as a number of contemporaneous species. Not only has it poor preservation potential in turbidite sandstones, very common in the thick Telychian sequences of mid-Wales, but also, a similar, but longer-ranging species, only distinguishable from R. maximus when complete and well-preserved, has been found here.